Beginning Jan. 17, the adult base fare for a ride on an MTA bus, on the subway system, or the Central Light Rail Line would rise from $1.10 to $1.25.

The proposal will be the subject of seven public hearings and must be approved by the secretary of transportation, who has ultimate authority over rates. While the proposal might be modified, a rate increase of some type is virtually certain.

It would be the second time in less than two years that the state transit agency has raised fares. The last time was on March 10, 1991, when the base fare rose from $1 to $1.10.

MTA Administrator Ronald J. Hartman said that the increase was necessary to comply with a 9-year-old state law that requires the MTA to recover at least half its operating costs from fares. The remainder is covered by tax revenue.

Raising fares will produce the money needed to offset the MTA's rising operating costs and decreasing returns from the fare boxes, Mr. Hartman said. But he also admitted that he would have preferred to wait until the economy improved.

"I agree that the timing stinks," said Mr. Hartman. "We've pushed this as far as we can, but we're up against the 50 percent recovery 'wall.' We're very nervous about that, frankly."

MTA officials said that the increase is almost certain to cause ridership to decrease further, perhaps by as much as 4 percent to 5 percent. And it is also likely to hurt most those who can afford it least -- low- and middle-income city residents who depend on public transit to get to and from work.

The decision comes even as the MTA is preparing to cut bu service by 5 percent, reducing frequency on some bus routes and discontinuing others. The specifics of that proposal are expected to be announced shortly, a spokesman said.

"We've never raised fares before at a time of a deep recession," Mr. Hartman said. "We could lose more riders than we expected."

Over the past two years, ridership on the Metro and MTA buses has declined about 4 percent a year. Officials blamed the decline on the economy.

Ronald R. Berndt, the MTA's assistant general manager for finance, noted that after modest increases in ridership in the 1970s and early '80s, the number of customers using mass transit has seemed to mirror city unemployment figures. As unemployment in Baltimore has risen, ridership has fallen in similar proportions, Mr. Brandt said.

Neither the costs nor the revenues associated with the light rail system, which opened for limited service in April and full-time in May, were a factor in the decision to increase fares, MTA officials said.

The state legislature has given the light rail a two-year exemption from the 50 percent cost-recovery formula to allow the system to expand its customer base.

Among MTA public transit systems, only the Maryland Rail Commuter (MARC) ridership has been growing in recent years. MARC trains provide an average 19,000 trips a day, and its

customers will not face fare increases.

Not counting light rail or MARC, the MTA's operating costs have risen 8.7 percent since June 30, 1990, a rate that state officials point out is less than the 11.4 percent rise in the Consumer Price Index over the period.

The rising costs are due mostly to employee wage and benefit costs. Although other state workers have been denied cost-of-living wage increases because of the state's budget crisis, the MTA's union employees have continued to get annual raises to offset inflation.

That benefit is due to a federal law that has protected the unions since the government took over Baltimore's private transit companies more than 20 years ago and which obligates the state agency to fulfill its union contracts.

This year, for instance, bus drivers, who average $15.50 an hour, received a 33-cent-an-hour raise. Light rail and Metro operators, mechanics, and transit police officers are also covered by union contracts.

The proposed increases would affect a variety of transit fares, from one-way fares for senior citizens, which will go up a nickel to 45 cents, to premium services. A trip downtown from the White Marsh Mall on a Park and Ride bus, for instance, would go up 30 cents to $2.15.

The change in the basic bus fare from $1.10 to $1.25 would keep the MTA in the middle of the pack among transit systems in the eastern half of the United States. Washington charges $1 for its base rate, while Philadelphia's fare is $1.50.

The MTA plans to discontinue its $3 tourist pass, which was good for one day and an unlimited number of rides, because it was not popular.